code: def add_reference_caption(self, sample_info, sample):
      reference_list = []
      for reference in sample_info["reference_tokens"]:
          text_processor_argument = {"tokens": reference}
          processed_reference = self.text_processor(
              text_processor_argument
          )
          reference_list.append(processed_reference["text"])
  
      # Restrict to minimum reference captions available per image
      sample.answers = torch.stack(reference_list)[
          : self.config.min_captions_per_img
      ]
  
      return sample
  
file_path: mmf/mmf/datasets/builders/coco/dataset.py
imports: import torch
  from mmf.common.sample import Sample
  from mmf.datasets.builders.vqa2 import VQA2Dataset
  from mmf.utils.distributed import byte_tensor_to_object, object_to_byte_tensor
label_desc: Use image node_id 4 for calling the COCODataset obj's underlying member method code with example usage: obj.add_reference_caption(sample_info, sample) and returns: sample